I have never had a CO2
system but have the same question as greenmagi. CO2
systems have two main parts: the solenoid valve, and the PH
controller. My thought is to skip the solenoid valve (about $70) completely:
Connect the PH
controller to the pump on a powered diffuser/reactor. When the PH
is low enough the controller turns off the reactor and the CO2
just bubbles up and out of the reactor and out of the tank.
I really think this plan will work except for one thing: can a 120V pump be plugged into a controller?